Hydrophobic polymers, in particular fluoropolymers, have been used for preparing porous membranes, for example, microfiltration membranes or ultrafiltration membranes, in view of their desirable bulk properties such as mechanical flexibility, thermal stability, and chemical resistance. However, when used to filter water based fluids, the surfaces of such membranes need improvement in terms of hydrophilicity, wettability, and/or low protein adsorption.
Attempts have been made to improve the one or more of the above properties of fluoropolymer membranes. For example, high energy irradiation, sputtering, and plasma treatments have been employed to improve the hydrophilicity of fluoropolymer membrane surfaces. However, such attempts have produced membranes with insufficient improvement in hydrophilicity, or when they have sufficiently improved hydrophilicity, the membrane surfaces have been modified to such an extent that the solute rejection performance has been significantly degraded from the original membrane performance.
The foregoing shows that there exists an unmet need for a method of improving the hydrophilicity of fluoropolymer membranes without significantly affecting their performance characteristics.